Four-stroke engines have been widely applied to different small tools, for example, hand-held mowers, shearers and other backpack machines. Therefore, besides strict requirements on stability, low vibration and the lubricating system, the engine is also required to be simplified, light and convenient.
Prior four-stroke engines have the following questions: on one hand, the oil pipeline of the lubricating system is complex, which makes processing complex and results in high cost; on the other hand, structures of parts are also complex, which makes engines heavy. For example, the cam chamber of the prior four-stroke engine is separated and far away from the rocker chamber, such that the cam in the cam chamber needs a long metallic tappet to transfer power to the rocker in the rocker chamber. As a result, the rotating tappet vibrates and affects the stability and anti-noise performance of the engine. Moreover, the separated cam chamber and rocker chamber result in more parts, and increased engine weight and high cost.